Quantification of the dependency of radon emanation power on soil temperature

A study on the quantification of the dependency of the radon emanation power on soil temperature has been made using the accumulation method. The emanation from dry soil was studied at temperatures between −20°C and 45°C. A formula to calculate the radon emanation power as a function of the temperatures has been developed. The formula would contribute to the modeling of radon transport in soils and building materials.     

Estimating the radon emanation coefficient from crystalline rocks into groundwater.

A simple method is proposed to estimate the coefficient of radon emanation from crystalline rocks into underground waters. In these cases, the crystalline rock seems as both the source and the reservoir of the radon. The calculations are based on a formula proposed by Maché for determining the concentration of radon in underground waters. Due to the inaccuracy of estimating some parameters (e.g. porosity), the results have a significant error. The advantage of this method is its simplicity and the possibility of obtaining results in a relatively short time. The estimated values of the emanation coefficient for selected crystalline rocks of the Sudety Mountains (SW Poland) vary from 7 to 41%, and after considering the error resulting from the estimation of rock porosity, saturation and density, the values range from 5 to 60%. The highest values of emanation coefficient (41, 33 and 21%) have been obtained for rocks in areas of tectonic dislocations and the lowest ones are for rocks outside dislocation zones (9 and 7%). The calculations imply that the emanation coefficient of rocks may have a greater influence on radon concentration in underground waters than the contents of radium in the reservoir rocks.     

The radon emanation power of building materials, soils and rocks

The ²²²Rn emanation power of building materials, soil and rock samples is determined by collecting exhalated radon on activated charcoal. Median values are 0.2 for dry soils and stones, 0.06 for sand, 0.025 for bricks, 0.006 for ceramic tiles, 0.008 for mineral slag and 0.3 for gypsum. The emanation power of soil rises with water content, in accordance with literature. For water content above 10% the emanation power of soil is about twice as high as for dry soil.     

Radioactivity and radon emanation fraction of the granites sampled at Misasa and Badgastein.

The chemical composition was analyzed and the radioactivity, radon exhalation rate and emanation fraction were measured to investigate the characteristics of the granites sampled at Misasa and Badgastein, world famous for radon therapy. The Misasa granite was probably composed of quartz, albite and microcline. The Badgastein granite was probably composed of quartz and muscovite. The radon exhalation rates and emanation fractions of the Misasa granite were much higher than those of the Badgastein granite, regardless of the (226)Ra activity concentrations.     

A comparison between active and passive techniques for measurements of radon emanation factors

Some radon related parameters have been determined through two different techniques (passive and active) in soil and phosphogypsum samples. Emanation factors determined through these techniques show a good agreement for soil samples while for phosphogympsum samples appear large discrepancies. In this paper, these discrepancies are analyzed and explained if non-controlled radon leakages in the passive technique are taken into account.     

Measurement of radon emanation factor from granular samples: effects of additives in cement.

Two methods for radon emanation factor determination were performed and compared regarding their measuring accuracy: (a) by hermetically closing the sample in an airtight container and measuring the induced radon activity, and (b) by mixing charcoal and sealing the sample hermetically and after placing the sample in an open vessel with no charcoal addition, measuring each time the 226Ra content using gamma-spectrometry. Measurements of radon emanation factor of cement and pozzolanic additives, i.e. fly ash and phosphogypsum were also performed.     

Differences of natural radioactivity and radon emanation fraction among constituent minerals of rock or soil

We examined differences in the radioactive characteristics among the main minerals forming granite materials. Using a non-toxic high-density agent, minerals were separated from rock (granite–gneiss) and soil (weathered granite) samples. The natural radioactivity (²³⁸U and ²²⁶Ra) and radon emanation fraction of the minerals were then studied by gamma-ray spectrometry. The radon emanation fractions (27–43%) of the minerals from the soil were much higher than those (0.6–4.6%) of the rock minerals. Additionally, the emanation fractions differed greatly among the minerals separated from both the bulk rock and soil. These results were discussed in terms of the differences of surface area and radium distribution in the mineral grains. It was noticeable that a higher emanation fraction than expected for quartz was commonly observed in the rock and soil samples. We then estimated the contribution of each constituent mineral to the total radon exhalation from the bulk samples. The result depended not only on the radon emanation fraction, but also on the ²²⁶Ra activity and the mineral content. Furthermore, using the obtained data, we also discussed the effect of grain size on radon emanation and why this has been reported to vary markedly in previous studies.     

加气混凝土试块氡射气系数随含水率及环境条件变化的研究

目的 研究加气混凝土试块氡射气系数随含水率、温度和相对湿度的变化规律。方法 采用连续测氡仪和密闭累积腔体,测量加气混凝土试块在不同含水率(0~60%)、温度(10~40℃)和相对湿度(12%~95%)条件下的氡射气系数;并对测量结果进行回归分析,探讨氡射气系数(ε)与含水率(s)、温度(T)和相对湿度的变化规律。结果 加气混凝土试块的氡射气系数随着其含水率的增加呈对数型增长,ε=0.096·ln(s+2.43)+0.037,R²=0.952;加气混凝土试块的氡射气系数随着其温度的增加而增加,并呈线性增长关系,ε=0.002 45·T+0.060 1,R²=0.987;不同相对湿度下,加气混凝土试块的氡射气系数测量结果差异无统计学意义(P>0.05)。结论 含水率、温度变化对加气混凝土试块氡射气系数影响较大,在建材氡放射性危害评价与控制体系中应注意这些因素对加气混凝土试块氡射气系数的影响。     

The effect of grain size and teflon matrix on the energy dependence of thermoluminescent dosimeters

The photon energy dependence of response of four Teflon thermoluminescent dosimeters (lithium fluoride, lithium tetraborate, calcium sulfate and calcium fluoride) is studied as a function of grain size, with and without a Teflon matrix. The analysis was performed using a calculation model based on Burlin's general cavity theory. The results obtained show that the grain-size effect is more important at intermediate energies, and that the response of larger grain sizes is more energy dependent. The results also show that in the case of calcium sulfate and calcium fluoride, the Teflon matrix has a relatively small effect and, in the case of lithium fluoride and lithium tetraborate, it contributes to a decrease or increase in the grain-size effect respectively. The results are compared with experimental and theoretical results from other authors.     

氡析出对居室建材外照射剂量模型的影响

目的 研究氡析出对居室建材外照射剂量模型的影响,为准确评价建材放射性外照射危害提供依据。方法 分析建材中氡的析出机制,推导建材单位比活度²²⁶Ra所致外照射剂量率氡析出修正因子的数学模型,利用Matlab程序解析计算、探讨氡析出修正因子与扩散长度、氡面发射系数以及建材厚度的关系。计算、比较部分建材在修正与未修正氡析出影响下所致的吸收剂量率。结果 建材单位比活度²²⁶Ra所致吸收剂量率的氡析出修正因子与扩散长度、建材厚度不相关,与发射系数负相关,在数值上等于“1－F_Rn”（F_Rn为氡面发射系数）。在修正与未修正氡析出影响两种情况下,部分建材所致吸收剂量率的相对百分偏差为2.23%~10.02%。结论 建材氡的析出对其外照射辐射剂量模型有一定影响,可选取氡析出修正因子为“1－F_Rn”进行修正,从而更科学地评价建材外照射危害。     

土壤氡析出率影响因素及估算模型

目的通过对某定点处土壤氡析出率的长期测量观察,分析并总结环境因素对氡析出率的影响规律。方法使用ERS-2静电收集式氡采样测量仪,每次采样累积时间40min,每10分钟测量一次氡浓度,通过线性拟和求算出土壤表面氡析出率;利用已有的数学模型对测量结果进行估算和评价;同时测量环境空气的湿度、温度、土壤含水量和土壤氡浓度。结果春季土壤氡析出率平均值为(24·9±5·6)mBq/(m2·s),夏季平均值为(11·9±3·4)mBq/(m2·s)。结论在影响土壤氡析出率的诸因素中,湿度非常重要,而环境温度对氡析出率的影响相对较小;测量期间环境气压变化不明显,没有观测到气压对析出率的影响。开展土壤射气系数的研究,将有助于阐明多种环境因素对土壤表面氡析出率的影响。     

土壤物理性质对土壤氡浓度及地表氡析出率的影响

目的探讨土壤性质对土壤氡浓度及地表氡析出率的影响。方法在北京、贵阳、呼和浩特的31个测量点进行土壤氡浓度及析出率的现场实测。采集土壤样品，在实验室进行土壤镭含量、含水量、孔隙度和粒径分布等物理性质测量。用线性拟合方法分析了实测土壤氡、析出率数据之间的相关性，以及它们与土壤镭含量的关系。结果地表氡析出率与土壤氡浓度和土壤镭含量有正相关关系；土壤含水饱和度过高或过低均会使析出率和土壤氡浓度降低；贵阳地区土壤镭含量较高，但其粉砂黏土壤的特性使土壤氡浓度很难准确采样，导致结果偏低。结论地表氡析出率和土壤氡浓度虽然与土壤镭含量有正相关关系，但在实际环境中易受含水量等多因素影响，而且土壤氡浓度的准确测量受土壤特性限制较大。     

Unattached fraction and size distribution of aerosol-attached radon progeny in the open air

Unattached fractions of the radon progeny ²¹⁸Po and ²¹⁴Pb, size distributions for both unattached ²¹⁸Po and ²¹⁴Pb, and attached ²¹⁴Pb and ²¹⁴Bi, along with condensation nuclei (aerosol-particle concentrations), were measured in the open air of the city of El-Minia, Egypt. The measurements were performed with a wire-screen diffusion battery and a low-pressure Berner cascade impactor using standard methodologies. The results for parameters of derived distributions demonstrate that the distributions for the former (unattached ²¹⁸Po and ²¹⁴Pb) are nearly similar. The diffusion equivalent diameters (d_f) of ²¹⁸Po and ²¹⁴Pb were determined to be 1.4 and 1.55 nm with relative geometric standard deviations (σ_g) of 1.65 and 2.1, respectively. The latter distributions (attached ²¹⁴Pb and ²¹⁴Bi) are nearly identical. Most of the activities were associated with the aerosol particles of the accumulation mode. The mean activity median aerodynamic diameters (AMAD) of ²¹⁴Pb and ²¹⁴Bi have the same value of 380 nm but the relative geometric standard deviation of the log-normal distribution of ²¹⁴Pb shows a broader activity distribution than ²¹⁴Bi (σ_g = 2.2 for ²¹⁴Pb and σ_g = 2.05 for ²¹⁴Bi).     

Measurement of radon and radon progenies at the German radon reference chamber.

The activity concentration of radon in the environment can vary over five orders of magnitude. Radon and its progenies thus concern all people involved in radiation protection as well as in low-level experiments. In the German radon reference chamber at the PTB, radon and its progenies are measured with different systems for alpha- and gamma-spectrometry with the full set of environmental parameters, e.g. temperature, humidity and aerosol concentration being controlled. Control of air pressure is also possible by use of an extention chamber. The sampling and measuring technique for radon and its short-lived progenies at the German radon reference chamber are the basis for fundamental studies with regard to the understanding of the equilibrium factor and the unattached fraction of progenies. The facility also serves for the calibration of radon progeny detectors.     

我国部分地区土壤氡析出率的理论模型

目的 本研究旨在通过理论研究和实验验证初步建立我国部分地区土壤氡析出率的理论模型。方法 通过对氡在土壤中扩散理论的分析，建立土壤氡析出率数学模型，该模型考虑了土壤的镭含量、射气系数、孔隙度和含水饱和度等因素对氡析出率的影响。为验证此模型，我们在北京、贵阳和内蒙古3个不同土壤类型的地区，共30处进行了氡析出率及土壤相关物理性质的实际测量。结果 有近1／3的样品理论值与实测值吻合比较好。结论 实测结果初步显示出模型的有效性。笔者对误差分布规律及产生原因进行了分析，提出了今后土壤氡析出率模型的改进方向。     

Microwave liver ablation: influence of hepatic vein size on heat-sink effect in a porcine model

PURPOSE: To determine influence of hepatic vein size on perfusion-mediated attenuation in adjacent microwave thermal ablation. MATERIALS AND METHODS: With approval of the institutional animal research committee, seven Yorkshire pigs underwent percutaneous (n = 2) or open (n = 5) microwave liver ablation under general anesthesia. In each, multiple ultrasound-guided, nonoverlapping thermal lesions were created within 1 cm of hepatic veins in a 5-10-minute ablation at 45 W. After euthanasia, the liver was harvested and sectioned at 0.5-cm intervals and the degree of perivascular coagulation attenuation was graded on histopathologic analysis. Correlation between venous size (small, < or =3 mm; medium, 3-6 mm; and large, >6 mm) and attenuation grade was performed with use of the Spearman rank test. RESULTS: In 63 of 103 sections (61%)--29 of 37 (78%) small, 27 of 48 (56%) medium, and seven of 18 (39%) large veins--the thermal injury extended to the vein wall around the entire circumference of the coagulation front without distortion of the ablation margin. In 40 of 103 sections (38.9%), varying degrees of concave distortion of perivenous ablation margins were noted, with significant correlation between vein size and heat-sink extent (P < .01). However, thermal injury extended to the vascular wall in all sections without complete circumferential sparing of liver tissue. Around two thrombosed veins, thermal lesions encased the vessels, producing paradoxically convex ablation margins. CONCLUSIONS: Although the heat-sink effect was significantly dependent on hepatic vein size, the majority of pathologic sections exhibited no or minimal effect. Further study is required to assess clinical implications.     

International intercomparisons of integrating radon detectors in the NIRS radon chamber

An international intercomparison of integrating detectors was conducted at NIRS (National Institute of Radiological Science, Japan) with a 24.4 m³ inner volume walk-in radon chamber that has systems to control radon concentration, temperature and humidity.During the first intercomparison (05.2007) four groups participated from four countries and for the second intercomparison (10.2007) 17 participants were involved from 11 countries.Most of detectors are in good agreement with each other when compared to the radon level provided by the radon chamber. It appeared that the 70% of detectors are unified within the 20% margin of uncertainty.     

Buried emanation; the development of seeds for permanent implantation

PURPOSE: To chronicle the development of radioactive sources for permanent implantation. METHODS AND MATERIALS: Review of contemporary literature. RESULTS: The value of ionizing radiation in the treatment of malignancy was appreciated soon after Roentgen's and Becquerel's discoveries. Brachytherapy was developed to treat tumors that were poorly controlled by early X-ray equipment. Sources and techniques for permanent implantation were devised in the first quarter of the 20th century. CONCLUSIONS: Long before the creation of artificial isotopes, pioneering physicists and clinicians fashioned seeds from naturally occurring radionuclides and ingenuity.